Segmented print bar for large-area ovjp deposition

ABSTRACT

OVJP print bars are provided that include multiple print head segments, each of which includes a print head and which can be positioned relative to the substrate independently of each other print head segment. Accordingly, a more consistent head-to-substrate distance can be maintained even for substrates that are not uniformly planar.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional of and claims priority benefit toU.S. Provisional Patent Application Ser. Nos. 62/501,905, filed May 5,2017 and 62/597,605, filed Dec. 12, 2017, the entire contents of each ofwhich are incorporated herein by reference.

FIELD

The present invention relates to devices and techniques for fabricatingrelatively large-area devices including organic emissive layers, anddevices such as organic light emitting diodes and other devices,including the same.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting diodes/devices (OLEDs), organic phototransistors, organicphotovoltaic cells, and organic photodetectors. For OLEDs, the organicmaterials may have performance advantages over conventional materials.For example, the wavelength at which an organic emissive layer emitslight may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Alternatively the OLED can be designed to emit white light. Inconventional liquid crystal displays emission from a white backlight isfiltered using absorption filters to produce red, green and blueemission. The same technique can also be used with OLEDs. The white OLEDcan be either a single EML device or a stack structure. Color may bemeasured using CIE coordinates, which are well known to the art.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY

According to an embodiment, an organic light emitting diode/device(OLED) is also provided. The OLED can include an anode, a cathode, andan organic layer, disposed between the anode and the cathode. Accordingto an embodiment, the organic light emitting device is incorporated intoone or more device selected from a consumer product, an electroniccomponent module, and/or a lighting panel.

According to an embodiment, a print bar for organic vapor jet (OVJP)deposition is provide, which includes a plurality of print headsegments, each of which includes an OVJP print head; a plurality of flyheight distance sensors, each of which is configured to measure adistance between a substrate disposed below the print bar and a portionof at least one of the print head segments; and a plurality ofactuators, each of which is configured to adjust a position and/ororientation of one or more of the plurality of print head segments basedupon one or more distances between the substrate and the print barmeasured by one or more of the plurality of fly height distance sensors.The print head segments may be arranged in two rows in a directionessentially perpendicular to a direction of motion of the print barrelative to the substrate when the print bar is operated to depositmaterial on the substrate. The print head segments may be disposedwithin the rows such that print areas of each row of corresponding OVJPprint heads form a single printed column on the substrate when the printbar is operated to deposit material on the substrate. Each OVJP printhead may include an OVJP deposition nozzle in fluid communication with acarrier gas source and an organic material vapor source. Each actuatormay be connected to, and configured to control the position and/ororientation of, at least two of the print head segments. Alternativelyor in addition, each actuator may controls the position and/ororientation of at least two of the print head segments based upondistance measurements obtained by two or more of the fly height sensors.Alternatively or in addition, each actuator may control the positionand/or orientation of at least two of the print head segments based upona distance measurement obtained by at least one of the fly heightsensors. Each print head segment may be movable independently of eachother print head segment of the plurality of print head segments. Eachprint head segment may be movable at least in a direction essentiallynormal to the substrate independently of each other print head segment,such that the distance from each print head segment to the substrate isadjustable independently of the distance from each other print headsegment to the substrate. The print bar may include one or more gaschannels arranged to transport organic material and/or carrier gas tothe plurality of print head segments, one or more vacuum channelsarranged to remove material from a region between the print bar and thesubstrate when the print bar is operated to deposit material on thesubstrate, or any combination thereof. The print bar and/or each printhead segment mat include a cold plate disposed adjacent to a pluralityof the print head segments.

In an embodiment, a method of fabricating a device using organic vaporjet (OVJP) deposition is provided. The method may include operating theOVJP print bar as previously disclosed. For example, the method mayinclude operating a plurality of print head segments to deposit materialon a substrate, each of which includes an OVJP print head; receivingdistance measurements from each of a plurality of fly height distancesensors, each of which is configured to measure a distance between asubstrate disposed below the print bar and a portion of at least one ofthe print head segments; and actuating one or more actuators of aplurality of actuators to adjust a position and/or orientation of one ormore of the plurality of print head segments based upon one or more ofthe distance measurements. The print bar, print head segments, andcomponents thereof may be arranged in any configuration as previouslydescribed and as disclosed herein. For example, the print head segmentsmay be arranged in two rows in a direction essentially perpendicular toa direction of motion of the print bar relative to the substrate whenthe print bar is operated to deposit material on the substrate. Themethod further may include moving the substrate relative to theplurality of print head segments, the plurality of print head segmentsrelative to the substrate, or a combination thereof, in the direction ofmotion. The print head segments may be disposed within the rows suchthat print areas of each row of corresponding OVJP print heads form asingle printed column on the substrate when the print bar is operated todeposit material on the substrate. Each actuator may be operated tocontrol the position and/or orientation of, at least two of theplurality of print head segments. The method may include actuating atleast one of the actuators to control the position and/or orientation ofat least two of the print head segments based upon distance measurementsobtained by two or more of the plurality of fly height sensors. Themethod also may include actuating at least one of the actuators tocontrol the position and/or orientation of at least two of the printhead segments based upon a distance measurement obtained by at least oneof the fly height sensors. The method further may include moving atleast one of the print head segments independently of each other printhead segment. For example, the method may include moving at least one ofthe print head segments in a direction essentially normal to thesubstrate independently of each other print head segment, such that thedistance from the print head segment to the substrate is adjustedindependently of the distance from each other print head segment to thesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of an organic light emitting device that can befabricated using embodiments disclosed herein.

FIG. 2 shows an example of an inverted organic light emitting devicethat does not have a separate electron transport layer that can befabricated using embodiments disclosed herein.

FIGS. 3A and 3B show a schematic of a current-generation substrate andan example single rigid print head used to print the entire substrate.The print head and support structure is over 2.5 meters in length.

FIGS. 4A and 4B show a schematic elevation view of a print head andsubstrate. FIG. 4A shows a print head and a uniform gap between atheoretical perfectly flat substrate. FIG. 4B shows a non-uniform gapbetween the print head and a substrate with non-perfect flatness.

FIG. 5A shows a segmented print bar according to embodiments disclosedherein, with articulated print heads disposed over a non-planarsubstrate that are capable of maintaining a constant or near constantprint head to substrate distance.

FIG. 5B shows an example print bar with two rows of print headsaccording to embodiments disclosed herein, in which printing aperturesof each row of print heads are arranged so that a complete row isprinted with no overlap of printing apertures and no gaps betweenalternating rows of print heads.

FIG. 5C shows a schematic illustration of a rectangular print barincluding rectangular segments as shown in FIG. 5B.

FIG. 6 shows an example of a partial print bar according to embodimentsdisclosed herein having “T” shaped segments.

FIG. 7 shows an example of a partial print bar according to embodimentsdisclosed herein having triangular print head segments.

FIG. 8 shows an example of a print bar with leading and trailing coldplates with rectangular segments according to embodiments disclosedherein.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), are incorporated byreference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as ink jet and OVJD. Othermethods may also be used. The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processability than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention canbe incorporated into a wide variety of electronic component modules (orunits) that can be incorporated into a variety of electronic products orintermediate components. Examples of such electronic products orintermediate components include display screens, lighting devices suchas discrete light source devices or lighting panels, etc. that can beutilized by the end-user product manufacturers. Such electroniccomponent modules can optionally include the driving electronics and/orpower source(s). Devices fabricated in accordance with embodiments ofthe invention can be incorporated into a wide variety of consumerproducts that have one or more of the electronic component modules (orunits) incorporated therein. A consumer product comprising an OLED thatincludes the compound of the present disclosure in the organic layer inthe OLED is disclosed. Such consumer products would include any kind ofproducts that include one or more light source(s) and/or one or more ofsome type of visual displays. Some examples of such consumer productsinclude flat panel displays, computer monitors, medical monitors,televisions, billboards, lights for interior or exterior illuminationand/or signaling, heads-up displays, fully or partially transparentdisplays, flexible displays, laser printers, telephones, mobile phones,tablets, phablets, personal digital assistants (PDAs), wearable devices,laptop computers, digital cameras, camcorders, viewfinders,micro-displays (displays that are less than 2 inches diagonal), 3-Ddisplays, virtual reality or augmented reality displays, vehicles, videowalls comprising multiple displays tiled together, theater or stadiumscreen, and a sign. Various control mechanisms may be used to controldevices fabricated in accordance with the present invention, includingpassive matrix and active matrix. Many of the devices are intended foruse in a temperature range comfortable to humans, such as 18 C to 30 C,and more preferably at room temperature (20-25 C), but could be usedoutside this temperature range, for example, from −40 C to 80 C.

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

In some embodiments, the OLED has one or more characteristics selectedfrom the group consisting of being flexible, being rollable, beingfoldable, being stretchable, and being curved. In some embodiments, theOLED is transparent or semi-transparent. In some embodiments, the OLEDfurther comprises a layer comprising carbon nanotubes.

In some embodiments, the OLED further comprises a layer comprising adelayed fluorescent emitter. In some embodiments, the OLED comprises aRGB pixel arrangement or white plus color filter pixel arrangement. Insome embodiments, the OLED is a mobile device, a hand held device, or awearable device. In some embodiments, the OLED is a display panel havingless than 10 inch diagonal or 50 square inch area. In some embodiments,the OLED is a display panel having at least 10 inch diagonal or 50square inch area. In some embodiments, the OLED is a lighting panel.

In some embodiments of the emissive region, the emissive region furthercomprises a host.

In some embodiments, the compound can be an emissive dopant. In someembodiments, the compound can produce emissions via phosphorescence,fluorescence, thermally activated delayed fluorescence, i.e., TADF (alsoreferred to as E-type delayed fluorescence), triplet-tripletannihilation, or combinations of these processes.

The OLED disclosed herein can be incorporated into one or more of aconsumer product, an electronic component module, and a lighting panel.The organic layer can be an emissive layer and the compound can be anemissive dopant in some embodiments, while the compound can be anon-emissive dopant in other embodiments.

The organic layer can also include a host. In some embodiments, two ormore hosts are preferred. In some embodiments, the hosts used maybe a)bipolar, b) electron transporting, c) hole transporting or d) wide bandgap materials that play little role in charge transport. In someembodiments, the host can include a metal complex. The host can be aninorganic compound.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

Various materials may be used for the various emissive and non-emissivelayers and arrangements disclosed herein. Examples of suitable materialsare disclosed in U.S. Patent Application Publication No. 2017/0229663,which is incorporated by reference in its entirety.

Conductivity Dopants:

A charge transport layer can be doped with conductivity dopants tosubstantially alter its density of charge carriers, which will in turnalter its conductivity. The conductivity is increased by generatingcharge carriers in the matrix material, and depending on the type ofdopant, a change in the Fermi level of the semiconductor may also beachieved. Hole-transporting layer can be doped by p-type conductivitydopants and n-type conductivity dopants are used in theelectron-transporting layer.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial.

EBL:

An electron blocking layer (EBL) may be used to reduce the number ofelectrons and/or excitons that leave the emissive layer. The presence ofsuch a blocking layer in a device may result in substantially higherefficiencies, and or longer lifetime, as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the EBLmaterial has a higher LUMO (closer to the vacuum level) and/or highertriplet energy than the emitter closest to the EBL interface. In someembodiments, the EBL material has a higher LUMO (closer to the vacuumlevel) and or higher triplet energy than one or more of the hostsclosest to the EBL interface. In one aspect, the compound used in EBLcontains the same molecule or the same functional groups used as one ofthe hosts described below.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. Any host material may be used with any dopant so long as thetriplet criteria is satisfied.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies and/or longer lifetime as compared to a similar devicelacking a blocking layer. Also, a blocking layer may be used to confineemission to a desired region of an OLED. In some embodiments, the HBLmaterial has a lower HOMO (further from the vacuum level) and or highertriplet energy than the emitter closest to the HBL interface. In someembodiments, the HBL material has a lower HOMO (further from the vacuumlevel) and or higher triplet energy than one or more of the hostsclosest to the HBL interface.

ETL:

An electron transport layer (ETL) may include a material capable oftransporting electrons. The electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

Charge Generation Layer (CGL)

In tandem or stacked OLEDs, the CGL plays an essential role in theperformance, which is composed of an n-doped layer and a p-doped layerfor injection of electrons and holes, respectively. Electrons and holesare supplied from the CGL and electrodes. The consumed electrons andholes in the CGL are refilled by the electrons and holes injected fromthe cathode and anode, respectively; then, the bipolar currents reach asteady state gradually. Typical CGL materials include n and pconductivity dopants used in the transport layers.

As previously discussed, OVJP is a mask-less, solvent-less printingtechnology for relatively large area OLED devices such as displays. Inthis technique, OLED materials are heated to evaporation or sublimationtemperature and transported to a print head in a stream of carrier gas.Conventional OVJP print heads typically contain a number of apertures ornozzles that direct the vapor toward the substrate on which the OLEDmaterial is to be deposited. In display fabrication techniques,generally each aperture prints one row of display pixels. Print headsmay be multiplexed to form print “bars” that span the width of thesubstrate such that all rows of pixels may be concurrently.

OVJP is primarily of interest currently as a research tool. However,OVJP techniques have demonstrated the required linewidth andacross-pixel film thickness uniformity for use in manufacturing OLEDdisplays that use a side-by-side RGB pixel format. In mass productionsystems, it is desirable to keep the time to complete a manufacturingstep relatively low to maintain efficient overall production. The timebetween completed manufacturing steps is often referred to as the “TAKT”time. To achieve desirable TAKT time for OLED device production, a massproduction OVJP printer may need to print multiple pixels or pixel rowsin parallel. For example, the best TAKT time would be achieved if allrows of pixels were printed at the same time. As a specific example, acurrent 4K display would require 3,840 rows of pixels printedsimultaneously, spanning the width of the display. Six 55-inch displayscan be manufactured on a single current-generation 2.200 m by 2.500 msubstrate. In this case, the OVJP deposition system would span the 2.2meter width of the substrate and could print two displays or 7680 pixelssimultaneously. FIG. 3A and FIG. 3B show an example of acurrent-generation (“Gen 8”) substrate 300, a print head supportstructure 301, and a single monolithic print head 302 that spans thewidth of the display glass.

However, substrates used to manufacture devices such as large-paneldisplays are not perfectly flat, and a rigid print bar would not provideadequate control of the separation between the print heads and thesubstrate. Because of this, current OVJP-type techniques only allow forefficient and accurate deposition on a limited width of substrate in asingle pass. For example, most conventional OVJP-type techniques are notsuitable for deposition on large substrate, in some cases for substrateslarger than about 0.5 m square or equivalent, without using rasteringtechniques. To deposit on larger substrates, current techniquestypically use a single OVJP nozzle array that includes a large number ofdeposition apertures that is rastered across the substrate. For example,some configurations include up to 100 or more deposition apertures inthe OVJP nozzle array. The nozzle array may include sensors and motionactuators to accurately maintain the gap between the substrate and thenozzle array assembly as a whole. Such techniques are much lesssensitive to variations in fly height and thus to variations insubstrate flatness. However, they also require complex managementsystems and have relatively very high TAKT times.

Thus, to achieve a desired pixel width using OVJP-type systems, it wouldbe desirable for the distance between the substrate and the print headto be tightly controlled. To do so while accommodating variations in theflatness of the substrate, embodiments disclosed herein provide a“segmented print bar,” which is a device having multiple segments thatcan move independent of each other to maintain the required distancebetween the print head and substrate. Each segment may include one ormore OVJP print heads. Embodiments disclosed herein also may allow forsignificant movement of the print head only in the y-direction (in thesubstrate plane and perpendicular to the direction of movement of thesubstrate), whereas conventional OVJP systems require significantmovement in both x- and y directions in order to raster the nozzle overthe substrate. Prior to development of the embodiments disclosed herein,it has not been considered feasible to use OVJP-type techniques to printlarge-scale substrates as disclosed herein. Accordingly, prior andconventional systems excluded any consideration of fly height adjustmentduring material deposition, and did not include any mechanism for makingsuch adjustments.

As a specific example, a 55-inch 4K display pixel is approximately 50 μmin width. Linewidths obtained using OVJP print heads are on the sameorder as the width of the jetting aperture and the distance from the jethead to the substrate. Accordingly, for OVJP techniques to attain aprinting width of about 50 μm, the fly-height separation between theprinting aperture, or print head, and the substrate should be accuratelymaintained to within +/−5 μm of the target fly-height or better. Thatis, the distance between the edge of the print head aperture and theclosest surface of the substrate should vary by no more than +/−5 μmduring deposition of material from the print head to the substrate.Deviations in fly height of more than +/−5 μm in either direction maywiden the deposition line so that it impinges on neighboring pixels, ormake the line thickness out of specification for the pixel size. Toprint a display on a current-generation glass substrate as previouslydisclosed with dimensions of 2.2×2.5 m, with a thickness of 0.5 mm, theprint head would need to be at least 2.2 m long, as shown in FIG. 3A,and the glass would need to be planar to within +/−5 μm to maintain theproper fly height.

However, as previously noted, current-generation glass substrates areexpected to have some variation in flatness of the surface. For example,current-generation display glass typically has a maximum deviation froma planar surface of about 40 μm. As a specific example, Corningindicates that Lotus NXT Glass® has the specifications shown in Table 1.

TABLE 1 Maximum Size Gen10 Substrate Major Thicknesses 0.3 mm, 0.4 mm,0.5 mm, 0.6 mm, 0.7 mm Thickness Tolerance ±0.02 mm Thickness Ranges  ≤9μm (150 mm Moving Window) Edges R-Beveled Corner Cuts 1.5 ± 1.0 mmOrientation Corners Various Squareness  ±0.3 mm Sheet Warp ≤0.20 mmWaviness Cut off: 0.8-8 mm ≤0.06 μm Cut off: 0.8-25 mm ≤0.33 μm

As another example, Schott Glass provides the “moving window size” shownin Table 2, which is a measure of glass flatness.

TABLE 2 Moving Window Size (mm) Thickness Change (μm) 150 9 (max) 25 4(max) 10 1.1 (typ) 5 0.7 (typ) Thickness range ± 20 μm over entiresubstrate

The specific values in Tables 1 and 2 are provided by way of exampleonly, and one of skill in the art will recognize that the flatnessspecifications in Table 1 are for an older generation of substrateglass, while the values in Table 2 are for a current generation ofsubstrate glass.

A flat printing bar that spans the width of such a display or asubstrate will have a maximum deviation in print head-to-substratedistance equal to at least half the maximum substrate deviation, i.e.,20 μm in this example. Accordingly, a conventional one-piece solid printbar would not be capable of holding the desired separation of +/−5 μmduring printing.

FIG. 4A shows a cross section of an example 2.2 m print head and aperfectly flat glass panel substrate. The print assembly 400 spans thewidth of the substrate 401. A support structure 403 for the print head402 is wider than the substrate so that the print head can span theentire width of the substrate. The fly-height gap 405 between thesubstrate 401 and the print head 402 is uniform across the width of thesubstrate. However, as previously noted, real substrates are notperfectly flat and the gap will not be uniform across the width of thesubstrate. FIG. 4B shows a schematic example of a 2.2 m long print baras previously disclosed, and a glass panel 406 having deviations inflatness of up to 40 μm. The resulting deviations from the ideal flyheight are labeled at 407, 408. The variation in fly height is found tobe in proportion to flatness specifications in Table 1.

As suggested by FIG. 4B, it has been determined that to maintain aproper fly height, the print head must be capable of conforming thetopography of the substrate glass or otherwise adjusting tonon-uniformities in the flatness of the substrate.

Embodiments disclosed herein provide a print bar having multiplesegments, each including a print head, which can be translated (e.g.,moved up and down relative to the substrate) and/or rotated (e.g.,tilted relative to the substrate) individually and independently of oneanother. FIG. 5 shows an example of such a device, in which segmentingthe print bar into smaller print heads that can be moved independentlyof one another allows the separation between the substrate and eachprint head to be maintained at a desired value. An edge-on schematicview of an example substrate is shown. Deviations to the flatness fromplanar are exaggerated, and a schematic profile of the segmented printbar shows how individual segments 502/503/504 articulate to follow theprofile of the substrate.

As shown in FIG. 5, each segment may include a print head supportstructure 501, articulated mounting supports 502, print heads 503 andone or more aperture plates 504. Each articulated support structure mayinclude movable elements that respond to one or more sensors in eachprint head that measure the distance from the print head to thesubstrate. Any suitable distance sensor may be used. For example,differential pressure, acoustic, capacitive, infrared, laser,ultrasonic, optical, and/or other sensor types may be used. As aspecific example, a capacitive sensor as disclosed in co-pending U.S.application Ser. No. ______ (Docket No. UDC-1240US), the disclosure ofwhich is incorporated by reference in its entirety, may be used. Datafrom each sensor may be provided to one or more of the print headsegments and, based upon the measurement and the desired fly-height, theprint head segment may be moved relative to the substrate to achieve adesired position and/or orientation of the print head relative to thesubstrate. Alternatively or in addition, a single sensor array or devicemay be used to measure the distance from each print head to thesubstrate. For example, a digital imaging or video system in conjunctionwith image recognition software may be used to identify and measure theposition of each print head segment and provide feedback to thecorresponding support structure. Based upon a distance measured by eachsensor, the moving elements move the associated print head to maintain aconstant distance 506 between the bottom of the print head, such as thebottom aperture plate 504, and the substrate 505. Furthermore, eachsegment also may be tilted relative to the substrate, such as tomaintain a deposition aperture parallel to the substrate or a major axisof a deposition nozzle perpendicular to the substrate. In general, eachprint head may be oriented independently of each other print head so asto maintain it in the desired orientation at the desired distance fromthe substrate.

Each print head may include a fully-functional OVJP nozzle or similardeposition device. For example, each segment may include one or moreprinting apertures defined in a hard, inflexible material to maintaintheir shapes. For example, materials such as a metal, ceramic or siliconmay be appropriate. Each aperture may be a rectangular gas outlet or itmay have an arbitrary shape to produce a desired printed profile. Italso may be formed by multiple smaller apertures configured in a uniquepattern to print each line.

Each print head segment also may contain vacuum ports and apertures toremove carrier gas and excess organic material. Vacuum ports may be madein the same material as the gas outlet apertures.

Each print head segment may include a heater or may be in thermalcontact with a heater to prevent condensation of the organic materials.

Organic vapor, carrier gas and vacuum ports may be connected to theirrespective sources or pumps via appropriate tubing for transport.

More generally, each print head segment may include an OVJP print headand any necessary components and connections to operate as afully-functional print head independently of each other print head inthe segmented print bar.

In some embodiments, some or all of the individual print heads may be influid communication with common vacuum sources, organic materialsources, or the like, or each print head may be in communication withseparate sources.

In some embodiments, each print head segment may include two or moresensors to measure the distance between each end of the print head andthe substrate, thereby allowing for more precise positioning andalignment of the segment relative to the substrate.

A segmented print bar as disclosed herein may include gaps betweenadjacent segments. In some embodiments, gaps between segments may befilled by a second row of print head segments which are offset comparedto the first row to fill the gaps. FIG. 5B illustrates a two row printbar with equal length print segments. Individual print heads 551 withintegrated height sensors 552 are arranged in two rows 553, 554 so thatprinting zones of each row will print lines of pixels with no overlapand no gaps. Supply of organic material and or vacuum for the printheads may be supplied by a common source, by individual sources, orcombinations thereof as previously disclosed. Arranging the print barssequentially as shown in FIG. 5B also may provide additional room forvertical actuators and for small adjustment in the distance betweenprint heads to accommodate manufacturing tolerances in the substratebackplane or for thermal expansion of the substrate. A staggeredarrangement also may allow space for manifolds to mount the print die inthe segment. The manifolds typically are wider than the dies they carry,so they cannot be placed immediately adjacent to each other withoutleaving one or more pixel rows unprinted. By staggering two rows of theprint die, a complete display may be printed in a single pass withoutleaving any pixel rows unprinted.

In some embodiments, the width of a print head segment may be determinedby the local area flatness of the substrate, for example by a movingwindow size as shown in Table 2 and/or a waviness value as shown inTable 1. Such dimensions may be used to determine a minimum, optimal, oracceptable size of an individual print head in a segmented device asdisclosed herein. More generally, the maximum width of a print segmenttypically can only be as long as the distance on the substrate that hasa height variation equal to the fly height tolerance. For example, usingthe values from Table 2 as an example, a print bar with a 150 mm printsegment would be within the +/−5 μm tolerance with the given 9 μm (max)thickness change.

More generally, in embodiments disclosed herein, a print die length maybe determined based on the fly height requirement of the print headdesign, the resolution required by a display design, and the local areaflatness of the glass substrate. For current-generation Gen8-type glass,a typical print die length may be in the range of 75 to 100 mm.

Embodiments such as those shown in FIGS. 5B and 5C include rectangularprint head segments. Each rectangular print head segment may include oneor more distance sensors to measure the gap between the print die andsubstrate as previously disclosed, one or more actuators to adjust thegap between the segment and the substrate based on feedback from thesensors, and one or more other sensors, such as visual sensors, whichmay be used to align the print die to the features on the substrate.

For example, FIG. 5C show a schematic representation of a segmentedprint bar 560 as disclosed herein, as viewed from above the print headin a direction toward the substrate (not shown), or from the surface ofthe substrate looking along a line normal to the substrate toward theprint head 560. The segmented print bar 560 may include one or moresegments 561 as previously disclosed, each of which may be rectangularin shape. The substrate-adjacent surface of each print bar segment maybe thermally isolated from the print head and may be chilled to act as aheat shield 564 that prevents the heated elements of the print bar fromoverheating the substrate. In the example arrangement shown, eachsegment includes two fly height sensors 562, two fly height actuators563 (which may be disposed above the print segment surface relative tothe substrate thus may not be visible when viewed from the substrate)and a print die 565. As used herein, a print die such as the print die565 may include deposition, exhaust, confinement and other gasapertures. Such a die may be fabricated, for example, in silicon usingMEMS microfabrication techniques. The segments and print die may bearranged so that there are no gaps in the printed area as a substrate ismoved relative to the print bar in the direction 566. The chilledsurface is continuous except for small gaps between segments.

In some embodiments, fewer sensors and actuators and/or smaller segmentsmay be used. In addition, the motion of the leading and trailing printhead segments may be coupled. Such arrangements may provide a reductionin space, complexity and cost for a large scale OVJP system.

For example, in some embodiments, the print head segments may bedifferent shapes and/or placed in different arrangements that allow asingle sensor to be used for two segments, one leading and onefollowing, using the same staggering concept as previously shown anddescribed with respect to FIGS. 5B and 5C. Segment surfaces form chilledsurfaces which may limit the radiation of heat from the hot print dieand other heated parts of the print head to the substrate. Any largegaps between segments may allow too much thermal damage to the substrateand it may be desirable to minimize such gaps. Thus, the surface of asegmented print bar as disclosed may perform during operation of thesystem as a continuous chilled surface, while still providing sufficientdegrees of movement to follow the surface of the substrate and maintaina constant or essentially constant fly height as previously disclosed.

FIG. 6 shows an example segmented print bar according to an embodimentdisclosed herein, in which each segment 601 has a “T” shape. Thesegments 601 are configured so that each fly height sensor 602 andactuator pair 603 serves two print die 605—one leading die and onefollowing die in the staggered arrangement, with the direction ofmovement 620 relative to the substrate defining which die are considered“leading” and “following” relative to other die. That is, duringoperation of the OVJP deposition system, each fly height sensor mayprovide distance information for two segments, and/or each actuator 603may be used to adjust the distance and/or orientation of two segmentsrelative to the substrate. As a specific example, a fly height sensor602 a may provide height information that may be used to adjust anactuator 603 a to control the distance and/or tilt of the two segments601 a, 601 b shown in FIG. 6A. Aligning the fly height distance sensors,actuators, and print die edges may allow for more precise and accuratecontrol of the position of the die relative to the substrate than otherconfigurations. For example, by aligning two fly height sensors with theends of the print die and positioning the actuators in a similarlocation on the other side of the die, the positioning of each end ofthe die may be precisely controlled based on distance measurements thatare likely to accurately represent the distance of each end of the printdie from the substrate. A chilled surface 604 may provide a limitationon radiation of heat from the print die as previously described.

FIG. 7 shows another example of a segmented print bar 700 according toembodiments disclosed herein. This example uses triangular print headsegments 701. Similar to the configurations shown in FIGS. 5-6, theprint head 700 may include one or more height sensors 702, actuators703, and print die 705. Height sensors and/or actuators may be “shared”among adjacent segments as previously disclosed. In operation, thesegmented print bar 700 may be moved in a direction 710 relative to thesubstrate, i.e., such that the print dies 705 and the top/bottom edgesof the triangular print head segments 701 are perpendicular oressentially perpendicular to the direction of movement. A configurationas shown in FIG. 7 may be desirable in some designs and for someapplications due to the potentially greater compactness of the segmentedprint bar. However, although the triangular segments are potentiallymore compact than the rectangular segments previously disclosed herein,they may not provide as much tilt capability as “T” shaped segments andsimilar designs as described with respect to FIGS. 6A-6B.

FIG. 8 shows another arrangement of a segmented print bar according toembodiments disclosed herein. In this arrangement, rectangular-faceprint heads 801 may be arranged in multiple ranks, with front heads 802and rear heads 803 disposed in a lapped arrangement such that theindividual print heads partially overlap in a direction of movement 830relative to the substrate. As with previously-disclosed arrangements,actuators 804 and distance sensors 807, 808 may be used to adjust thedistance and tilt of individual print head segments relative to thesubstrate. For example, in the arrangement shown in FIG. 8, eachactuator 804 may transfer vertical motion to a rear corner 805 of afront-rank print head 820 and a front corner 806 of a rear-rank printhead 825. As in other arrangements disclosed herein, each actuator andthe articulations connecting it to the two print heads it services maybe disposed in line with the printing direction. Furthermore, fly heightsensors on the front-rank print heads 807 may each be associated with adifferent actuator, as previously disclosed in other arrangements, andin line with an associated actuator along the printing direction. Asecond set of fly height sensors 808 may be disposed on the rear-rankprint heads. This second set of fly height sensors 808 may improve theperformance of the segmented print head bar in bidirectional operation,since it allows the print heads to respond to changes in substrateheight relative to the depositors when moving rearwards with respect tothe substrate as well as forwards. The print head segments may besurrounded by a fixed cold plate 809 disposed to the front and/or rearof the segmented print heads. The cold plate may include extendedportions 810 (“fingers”) on the front and/or rear edges thatinterdigitate with the staggered line of print heads as shown. Such anarrangement covers the regions between the cold plates associated witheach of the individual print head segments and may further protect thesubstrate from heat generated by the OVJP mechanism. The cold platefingers may be separated from the print heads by small gaps 811 topermit motion of the segmented print heads as previously disclosed.

As used herein, when a print bar or other OVJP deposition apparatus anda substrate are described as being moved in a direction relative to eachother or moved in a relative direction, such as the directions 620, 710,830, and the like, it will be understood that such motion may beaccomplished by moving the print bar or apparatus and holding thesubstrate stationary, moving the substrate while holding the depositionapparatus stationary, or moving both components so as to achieve thedesired relative motion.

Embodiments disclosed herein provide a segmented OVJP-type print barthat includes multiple independent several print heads that may besuspended from a rigid support structure. The print bar segments providethe full functionality of a large print bar while solving the inabilityof a single monolithic print bar to maintain a constant printhead-to-substrate distance. Segmenting the print bar into multiplediscrete print heads as disclosed herein, each of which has a range ofmovement in the direction of the substrate, provides the ability of theprint system to compensate for the non-planarity of OVJP-suitablesubstrates.

Furthermore, a segmented print bar as disclosed herein also may havemore relaxed tolerances required for the print head bar itself whencompared to conventional print heads or a single print head bar used todeposit over the same surface area. For example, a very large print headbar (e.g., 1-2 m long or more) with a flatness tolerance of +/−5 μm orless and a similarly tight depositor placement tolerance from end to endwould be exceedingly difficult if not impossible to create usingconventional techniques. In contrast, using a segmented print bar asdisclosed herein allows for individual segments that may be sized tomeet the required tolerances. For example, components having dimensionsof 150 mm and smaller may be made by well-understood semiconductorfabrication techniques. Individual segments may be registered tofeatures on the substrate directly, making the process more tolerant toadditive tolerance errors in both the print head and substrate.

A segmented print bar as disclosed herein also may be advantageous incomparison to a single linear print bar because the printhead-to-substrate separation may be maintained over substrates that arenot perfectly planar. As disclosed herein, when the print head tosubstrate distance is not maintained at a constant desired value, theline width and deposition thickness may change and the deposition maynot be to specification, or even of sufficient tolerance to provideacceptable or even poor performance. In general, the deposited linebecomes too wide if the separation is too large, and the thicknessbecomes too great if the separation is reduced. Maintaining a correctseparation therefore may be essential to producing a printed line withthe desired width and thickness to achieve large-scale OLED fabrication.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

We claim:
 1. A print bar for organic vapor jet (OVJP) deposition, theprint bar comprising: a plurality of print head segments, each of theplurality of print head segments comprising an OVJP print head; aplurality of fly height distance sensors, each of the plurality of flyheight distance sensors configured to measure a distance between asubstrate disposed below the print bar and a portion of at least one ofthe print head segments; and a plurality of actuators configured toadjust a position and/or orientation of one or more of the plurality ofprint head segments based upon one or more distances between thesubstrate and the print bar measured by one or more of the plurality offly height distance sensors.
 2. The print bar of claim 1, wherein theplurality of print head segments are arranged in two rows in a directionessentially perpendicular to a direction of motion of the print barrelative to the substrate when the print bar is operated to depositmaterial on the substrate.
 3. The print bar of claim 2, wherein theplurality of print head segments are disposed within the rows such thatprint areas of each row of corresponding OVJP print heads form a singleprinted column on the substrate when the print bar is operated todeposit material on the substrate.
 4. The print bar of claim 1, whereineach OVJP print head comprises an OVJP deposition nozzle in fluidcommunication with a carrier gas source and an organic material vaporsource.
 5. The print bar of claim 1, wherein each actuator of theplurality of actuators is connected to, and configured to control theposition and/or orientation of, at least two of the plurality of printhead segments.
 6. The print bar of claim 5, wherein each of theplurality of actuators controls the position and/or orientation of theat least two of the plurality of print head segments based upon distancemeasurements obtained by two or more of the plurality of fly heightsensors.
 7. The print bar of claim 5, wherein each of the plurality ofactuators controls the position and/or orientation of the at least twoof the plurality of print head segments based upon a distancemeasurement obtained by at least one of the at least one fly heightsensor.
 8. The print bar of claim 1, wherein each print head segment ofthe plurality of print head segments is movable independently of eachother print head segment of the plurality of print head segments.
 9. Theprint bar of claim 8, wherein each print head segment is movable atleast in a direction essentially normal to the substrate independentlyof each other print head segment such that the distance from the eachprint head segment to the substrate is adjustable independently of thedistance from each other print head segment to the substrate.
 10. Theprint bar of claim 1, further comprising one or more gas channelsarranged to transport organic material and/or carrier gas to theplurality of print head segments.
 11. The print bar of claim 1, furthercomprising one or more vacuum channels arranged to remove material froma region between the print bar and the substrate when the print bar isoperated to deposit material on the substrate.
 12. The print bar ofclaim 1, further comprising a cold plate disposed adjacent to aplurality of the print head segments.
 13. A method of fabricating adevice using organic vapor jet (OVJP) deposition, the method comprising:operating a plurality of print head segments to deposit material on asubstrate, each of the plurality of print head segments comprising anOVJP print head; receiving distance measurements from each of aplurality of fly height distance sensors, each of the plurality of flyheight distance sensors configured to measure a distance between asubstrate disposed below the print bar and a portion of at least one ofthe print head segments; and actuating one or more actuators of aplurality of actuators to adjust a position and/or orientation of one ormore of the plurality of print head segments based upon one or more ofthe distance measurements.
 14. The method of claim 13, wherein theplurality of print head segments are arranged in two rows in a directionessentially perpendicular to a direction of motion of the print barrelative to the substrate when the print bar is operated to depositmaterial on the substrate, the method further comprising moving thesubstrate relative to the plurality of print head segments, theplurality of print head segments relative to the substrate, or acombination thereof, in the direction of motion.
 15. The method of claim14, wherein the plurality of print head segments are disposed within therows such that print areas of each row of corresponding OVJP print headsform a single printed column on the substrate when the print bar isoperated to deposit material on the substrate.
 16. The method of claim13, wherein each actuator of the plurality of actuators is connected to,and configured to control the position and/or orientation of, at leasttwo of the plurality of print head segments.
 17. The method of claim 16,further comprising actuating at least one of the plurality of actuatorsto control the position and/or orientation of the at least two of theplurality of print head segments based upon distance measurementsobtained by two or more of the plurality of fly height sensors.
 18. Themethod of claim 16, further comprising actuating at least one of theplurality of actuators to control the position and/or orientation of theat least two of the plurality of print head segments based upon adistance measurement obtained by at least one of the at least one flyheight sensor.
 19. The method of claim 13, further comprising moving atleast one of the plurality of print head segments independently of eachother print head segment of the plurality of print head segments. 20.The method of claim 19, further comprising moving at least one of theplurality of print head segments in a direction essentially normal tothe substrate independently of each other print head segment of theplurality of print head segments such that the distance from the atleast one print head segment to the substrate is adjusted independentlyof the distance from each other print head segment of the plurality ofprint head segments to the substrate.